The invention relates to an electronic-hydraulic control device of an automatic automobile transmission in, which frictional clutches or brakes that can be engaged or released are controlled to shift individual gears by pressurizing the actuators depending on the operating parameters of the automobile transmission and a drive motor as well as on devices for influencing the gear shift operation and/or drive program.
An electronic-hydraulic control device of an automatic automobile transmission of the type described above is known from EP 0 440 748 B1. In this control system a control valve is associated with each actuating device and the solenoid valves and shifting valves, which are used to drive the control valves can perform multiple functions. The control device of this transmission control has a fault-monitoring device in which an associated solenoid valve or pressure control valve is controlled in such a way when the error signal appears that the automobile transmission is in idle at least phasewise. An automobile must be able to continue traveling even if there is a defect in the electronic control.
The goal of the invention is to create an electronic-hydraulic transmission control for an automatic transmission, preferably a six-speed transmission, in which the clutches or brakes of the transmission can be controlled by an electronic control device and in which an emergency gear is automatically selected if the electronic control device fails, which is designed such that when traveling in the upper transmission speeds (4 to 6), a higher gear is selected in case of failure, and during travel in the lower speeds (1 to 3), a shift is made to a lower gear in the event of a defect.
This goal is achieved by a type-compliant electronic-hydraulic transmission control with the characterizing features of the main claim in which the clutches or brakes can be controlled directly by the electronic control device by driving electrical pressure control valves or electrical solenoid valves which in turn control hydraulic valves that pressurize the clutches or brakes depending on the control pressure of the electrical pressure control valves. The solenoid valves or electrical pressure control valves in the de-energized state always assume a predetermined position in which the emergency gear is selected by corresponding valve combinations. This is necessary since even when the electronic control device fails, travel must still be possible. By the solenoid valves and electrical control valves assuming a predetermined position in the de-energized state in an emergency case, the clutch or brake to be engaged for the emergency gear is not subjected to a controlled pressure but to the full system pressure. In order to prevent thermal loading of the emergency gear clutches, the shift from the previous gear to the emergency gear must not be too high. For this reason, the control valves are switched so that in case of a previously used upper gear, preferably the fourth to sixth gear, in case of an upper gear, the fifth gear is selected, and during travel in the lower gears, preferably one to three, a shift is made to a lower gear, preferably the third gear. Reverse can be selected directly during the emergency operation by shifting the selector lever. Since gears can no longer be shifted when traveling in an emergency gear, it is possible that when the fifth gear is engaged as the emergency gear, the vehicle can no longer start in this fifth gear, for example after braking at a traffic light. By lowering the system pressure shortly to zero, for example by switching off the combustion engine, the control valves are switched so that when re-starting the combustion engine, the third gear is automatically selected when the electronic control device is defect. Since this electronic-hydraulic transmission control is preferably used for a six-speed automatic transmission, the control valves controlling the clutches and brakes are designed with two different valve characteristic curves. This is necessary since in a six-speed automatic transmission, the clutches or brakes must be operated at different speeds in order to shift gears in combination with other clutches or brakes. Thus a clutch is actuated in both the third and fifth gear for engaging the gears. However, since the torque on the clutch in a lower gear is different from the torque of the same clutch in an upper gear, it is necessary to subject the actuator of this clutch to different pressures depending on the speed selected.
Depending on the gear combination, the control valves are either pressurized by only one surface or, if a second valve characteristic curve is required, the control valves are pressurized by another surface, with the surface of one pressurized side being different from the other side. This results in a different clutch pressure while the control pressure remains the same.